This invention concerns the handling of volatile liquids. In particular, the invention relates to apparatus for use in the filling of a substantially closed tank with a volatile liquid, and also to methods for filling such a tank. The invention further relates to a tank including a fill-pipe.
Though the present invention is applicable to the handling of a wide variety of volatile liquids, it finds a particular application in the filling of a storage tank with petroleum spirit (petrol) such as a storage tank of a petrol filling station used by motorists. The invention will consequently be described hereinafter solely with reference to such application, though it is to be understood that the invention is not to be regarded as limited to this.
It is well known that there are wet stock losses associated with the storage tanks of a petrol filling station--that is to say, the metered amount of petrol delivered to purchasers is always less than the metered amount of petrol supplied to the storage tank from a road tanker. The losses generally are attributed to the volatility of the petrol and in particular vapour losses during delivery of the petrol to the storage tank, the holding of excessive stocks and a temperature differential between petrol already in a storage tank and petrol delivered from a road tanker--which latter is usually significantly higher than petrol already in the storage tank.
Good site management may minimise losses associated with excessive stock holdings. Little can be done about the delivery of petrol at a higher temperature than petrol already in the tank, since that largely depends upon the ambient temperature. The present invention aims at addressing the losses associated with delivery of the petrol into the storage tank.
A filling station underground storage tank is essentially wholly sealed, except for the required openings to allow the delivery and withdrawal of petrol. There may also be one or more further openings through which telemetry equipment may be inserted into the tank. These openings are normally provided in the lid of a manhole at the top of the tank and precautions have to be taken whenever pipes are to be connected to or disconnected from these openings If the tank is to be opened by removal of the lid, extreme precautions have to be taken to ensure the risk of explosion is minimised--and a filling station may be out of service for perhaps 48 hours in the event that a tank has to be opened.
The delivery of petrol is usually performed by connecting a flexible pipe from a road tanker to a fill-pipe passing through the lid and extending downwardly into the tank. Whenever petrol is delivered, there will be very significant turbulence within the petrol already in the tank, leading to the generation of large quantities of vapour. Moreover, the turbulence of the petrol within the tank has a scouring effect on the walls of the tank, leading to the production of scale which has to be filtered out of the petrol withdrawn from the tank.